1. Field of the Invention
The present invention relates to a vacuum pumping device, particularly of the type comprising a turbomolecular pump.
As it is known in the art, a turbomolecular vacuum pump comprises a plurality of pumping stages housed within a substantially cylindrical casing and provided with an axial inlet port of the pumped gases located at one end, and with a radial or axial exhaust port of the gases located at the opposite end of the cylindrical casing.
The pumping stages generally comprise a rotor disk, secured to the rotating shaft of the pump, that is driven by an electric motor at a speed usually not lower than 25,000 rpm and in some cases as high as 100,000 rpm.
The rotor disk rotates within stator rings fastened to the pump casing and defining the stator of the pumping stage, with a very small gap therebetween. In the space between a rotor disk and the associated stator disk a pumping channel of the pumped gases is defined.
The pumping channel defined between the rotor and the stator in each pumping stage communicates with both the preceding and the subsequent pumping stages through a suction port and an exhaust port, respectively, provided through the stator in correspondence with the pumping channel of the pumped gases.
A turbomolecular pump of the above type is disclosed, for example, in the U.S. Pat. No. 5,238,362 assigned to the assignee of the present invention. The turbomolecular pump described in U.S. Pat. No. 5,238,362 employs both pumping stages provided with rotors formed as flat disks and pumping stages provided with rotors equipped with blades. This combined arrangement of pumping stages results in a very good performance of the pump in respect of the compression ratio, while allowing the gases to be discharged into the outer environment at atmospheric pressure by means of simple pre-vacuum pumps without lubricant, such as diaphragm pumps. Moreover the construction of a vacuum pump of the turbomolecular type as taught by the U.S. Pat. No. 5,238,362 allows for a considerable reduction of the pump power consumption.
It has been suggested to employ electronic control units or controllers for feeding the electric motor of a vacuum pump in general, and more particularly of the turbomolecular type, such pumps being equipped with an electronic feeding circuit adapted to generate a voltage system for feeding the electric motor that rotates the vacuum pump.
Generally such control unit comprises means for converting the available AC mains voltage into the rated voltage level suitable for the operation of the vacuum pump motor, and means for adjusting the feeding voltage level during the pump working cycle on the basis of the residual pressure within the vacuum pump and the operating conditions of the pump motor, from the starting condition to the steady state rotating condition.
Because of the overall size and the cooling requirements, the known unit must be mounted separately from the turbomolecular pump and be equipped with dedicated cooling devices in addition to those already provided for cooling the pump.
The provision of a control unit separated from the vacuum pump, to be independently cooled and electrically connected both to the mains and to the vacuum pump by conductors of suitable length and cross-section, is an inconvenience preventing the construction of vacuum pumping devices that are compact and of small size.
2. Summary of the Invention
Therefore it is an object of the present invention to provide a vacuum pumping device, particularly of the turbomolecular type, that is compact and of small size.
In accordance with the present invention there is provided a vacuum pumping device which comprises a vacuum pump having a casing with a suction port and an exhaust port therein. The casing comprises a first portion and a second portion. The first portion houses gas pumping stages which are formed by rotor disks secured to a rotating shaft and stator rings secured to the casing. The second portion comprises an electric motor and at least one bearing for supporting the rotating shaft.
The vacuum pumping device also comprises an electronic control unit having a housing which forms an inner space therein. The housing comprises electronic components which are placed within the inner space. These electronic components form an electronic circuit for feeding the electric motor of the vacuum pump.
The second portion of the casing of the vacuum pump is placed within the inner space of the housing of the electronic control unit. The electronic components are disposed within the housing between an outer surface of the second portion of the casing and inner walls of the housing. The vacuum pumping device fan generates an air flow for cooling the electronic components and the second portion of the casing within the inner space of the housing.
The fan can be disposed outside or within the housing of the electronic control unit. If the fan is positioned outside the housing, the air flow generated by this fan is divided into two portions: one portion of the flow is directed toward the first portion of the casing, while another portion of the flow is directed towards the housing for cooling the electronic components. A liquid cooling system may be incorporated to the vacuum pumping device as an alternative to an air cooling system.
The electronic circuit comprises a sensor for sensing the temperature within the housing which is in a thermal contact with the second portion of the casing of the vacuum pump.
Further characteristics and advantages of the invention will become evident from the description of some preferred exemplary but not limiting embodiments of vacuum pumping devices illustrated in the attached drawings in which: